Frequency control apparatus and method



July 13, 194s.

A, E. HARRISON Filed July 30, 1943 '14 x4/r2 M1213 16M/2mm /55 f, .541 l 270 m- SoU/@c5 35 FREQUENCY n 7/ 7 l l) f3@ fl 3. 7571 3 .57V

EXC/75K FREQUENCY f sol/RCE Ml/L A T/N VOL 7A 6E INVENTOR ARTHUR #ARR/50N ATTORN EY Patented July 13, 1948 `s PATENT ori-lcs FREQUENCY CONTROL APPARATUSV AND METHOD -Arthur E. Harrison, Rockville Centre, N. yY., assignor toThe Sperry Corporation, a corporation of Delaware Application July 30, 1943, Serial No. 496,716 Y' 26 Claims.

I'llisv invention relates to microwave apparatus and methods and is especially concerned with apparatus and methodsfor accurately obtaining ultra high frequencies especially for measurement, Astandardization and like purposes,

. Microwave apparatus has developed to the eX- tent where there is need for accurate frequency measurement, and for setting up reliable primary andsecondary frequency standards. In` some known crystal-controlled frequency multiplier microwave devices of .the lcavity resonator type, alimitedvnumber of; different frequencies may be accurately obtained by resonator tuning adjustment, but to obtain further frequencies it is necessary to change crystals or make other extensive adjustments or both. The present inven tion isintended to provide a source of a much larger` number 'of obtainable ultra high frequencies than are available in -such4 known sources.v

if yIt is a major object of this invention to provide no vel ultra high frequency methods and apparatus fory selectively obtaining and reproducing any of a large number of distinct frequencies accurately.

A further object ofthe invention is to provide novel methods and apparatus for accuratelyobtaininga sequence of desired discrete ultra high* frequencies from `a cavity resonator device.

, A further object of the invention is to provide novel methods and apparatus for energization ofv microwave devices of the cavity resonator type:

rA further object of the invention is to rprovide novel cavity resonator apparatus wherein electron concentration or groupingy in the electron beamx` is phase modulated, so that the apparatus may be tuned to selectively produce any of a large number ofrationally related frequencies, such as sideband or harmonic frequencies or both, which canbe separably extracted for desired utilization. Further objects of the inventionwill presentlyl appearas thedescription proceeds in connection with the appended claims and the annexed drawing wherein:

Fig. lis a combination schematic and diagrammatic View usefulfor illustrating apart of the principles of the invention;

l Fig. 2 is a diagrammatic view'illustrating the relation Vof the carrier and some sideband frequencies obtainable from the apparatus of Fig, 1; Fig, 3 is a diagrammatic view illustrating carrier and sideband output relations obtainable from the apparatus of Fig. 1; f

;E'g.4 is a kfurther schematic .and diagram-- matic view illustrating Ythe invention as applied to a frequency multiplier device of the cavity resonator type; and

Fig. 5 is a diagrammatic viewillustrating sideband and harmonic frequency relations obtain-` able from the apparatus of Fig. 4.

Fig. 1 illustratesv a vpart of the principles Aappli-v cable to the invention employs a conventional two-resonator amplifier of the velocity modulation type wherein aybeam'of electrons is pro.-

jected from a cathode II through hollow con-V ductive input and output resonators kI2 and I3. The cathode is heated by a suitably energized lament I4, and enclosed by a glass wall I5 sealed in vacuum tight relation to resonator I2.

.Resonators I2 and I3 are interconnected bya` rigid drift passagetube I6. Inputgrids I1 and I8 are provided the path of the beam in a, wallof resonator I2 and the adjacent end of tube I6. Output vgrids I9 and 2l are provided in the path ofthe beam in a wall of resonator I3 and the adjacent end of tube I,6, A suitably shaped collector electrode 22 seals oi resonator I3 about gridls.

One'end wall portion 23 of resonator I3 is an-V nularly crimped so'as to be flexible, whereby' relative'separationof grids 2| .and I9 and variation of.

the naturalfrequency of resonator I3 may be accomplished by adjustment offscrewsg24` reacting against 'asupport 25 xed with tube I6, screws24 being threaded in a mount 26 fixed tothe body of resonator I3. Thus resonator I3 may be tuned to different ,natural frequencies by alteration of physicialcharacteristics such as its volume and internal shape by adjustment of screws 24. The

unidirectional accelerating voltage for cathode I I! is Aderived' from battery 21 having its negative ter-v minal connected to cathode II and itspositive terminal connected to grid I'I through ground andy resonator I2. A suitable `alternating voltage source of modulation frequency 28 is connected to the cathode through a condenser 29 Vwhich blocks'voff unidirectionalr current from battery Resonator `I2is excited by Vhigh frequency Yen'- ergy transmitted Vfrom a suitable source 3l by coaxialr line 32.* The output of resonator I3 is eX- tracted by coaxialiline 33. Sources 28 and 3I'may comprise any suitable, preferably stabilized,sources of alternating volt'- age having 'accurately controllable'frequencies. The modulation frequency from source 28 is substantially lowerithan the exciting frequency` from source3l. Y Ingoperationgwhile the electron beam from cathode yII isrpassing between grids I'I and I8 of resonator I2, the electrons in the beam are alternately accelerated and retarded, or velocity this action being also known as*velocitygroup-` ing along the beam.

The electron concentrations in density, or electron bunches or groups as they are sometimes.

called, in the beam arrive at output grids 2 I., and I9 with a repetition rate equal to the frequency of resonator I2, and represent an electron current of that frequency having a phase relation with respect to the input resonator -Wave Whichisa function of and determined by thetransi-t'time between the resonators I2 and I3.

The spacing of the electron groups or bunches along the beam is determined by the carrier frequency of the vfield `Within resonator I2 and the initial electron velocity. In usual cavity resonator amplifier operation, the beam acceleration voltage is constant, so that the length of tube I can be selected to obtain optimum interaction betvveen'the electronbeam-'and the field within resonator |13. l

This velocity grouped electron beams, in passing between output'grids 2| and I9, excites oscillations Within -resonator I3, andthe alternating field within resonator I3 extracts energy from the beam. .This extracted energy sustains oscillationswithin resonator I3 yand is availablefor output. on line :33. The frequency of this extractedr energ-yisdetermined. by the above described rate cnf-repetition of the electron bunching in the beam, which in usual amplifiers of this type is the inputorcar-rier frequency. As in usual amplier operation,v screw '24 is adjusteduntil. the natural frequency of resonator I3 corresponds to this carrier frequency vfor `optimum output.

, In general, the above described operation-is the same as` described: in Varian Patent No. 2,242,275, to: which reference is made for'further detail.

`Inaddition tothe available output. carrier fre-v quency, `there is :available inthe Ygrouped-beam a ldesired sequence of other' discrete frequencies which may be obtained by suitably tuning resonator I3. These other frequencies, which are notV available in the usual amplifier output, are made available .in the beam vby the modulation.Y action of source28.

The modulation voltagefrom :source 28,-. causes variation ofthe beam acceleration voltage at the modulation -frequency,-and thereby correspondingly varies the initial velocities and the transittimes of the electrons in the beam. This modulation therefore correspondingly'varies the phase l ode II and grid Il, or on'a cylindrical or other 'suitably shaped electrode insulatingly mounted in tube I6. These proposed modifications are Vequally applicable to the apparatus shown in Fig.

4 and discussed'hereinafter.

The above described modulation effects producean available output from the phase modulated grouped beam which consists of the carrier frequency and an infinite Sequence of sum and difference sideband frequencies spaced at intervals equal tothe modulation frequency. Suitable tuning of resonator I3 makes thevcarrier or any of those side band frequencies Within the tuning range of resonator I3 selectively available on line 33. Screws Zll are simply adjusted until the natural frequency of resonator I3 corresponds to the desired sideband frequency. By maintaining the modulation frequency high as compared to the band width permitted by the Q of resonators I2 and I3, there will be substantiallyno output on line 33 except the carrier or the particular sideband for which resonator I3 is tuned. The tuning mechanism can be suitably calibrated for selecting sidebands correspondingto a par ticular modulation frequency.

Fig. 2 shows diagrammatically the spacial-relation between the carrier frequencyF and typical sideband frequencies indicated in dottedlincs, available in the oput of the apparatus of'Fig. 1.

Fig. 3 illustrates typical curves showing graphically the relation between the amplitudes of the carrier and sideband frequencies obtainablel by the apparatus of Fig, l as a function ofl the modulation voltage. These curves were made from tests using a cavity resonator type-amplier similar to Fig. 1. Curve A represents the carrier or normal operating frequency Vof the amplifier, while curves B, C and D represent respectively rst, second and third sideband frequencies having in this instance 50 megacycle per second separation. The sideband maxima are clearly distinct and tunably separate, and their approximately equal amplitude is indicated. The output milliamperes were measured ythrough a crystal connected at line 33, while the modulation voltage was Athat superposed on the cathode acceleration voltage.

Fig. 4 illustratesthe invention as embodledin a cavity resonator type multiplier device 34 which comprises/input and output resonators 35 and 36. A drift tube 3l extends between theresonators, being coupledI to resonator 35`by a relatively high capacity section `4l] for reducing the necessary size of resonator 35. A cathode 38,lfxeated by a lament39 energizedfrom a suitable-source 4I, is arranged to project'a beam of' electrons through the resonators35 and 36.

Resonator 36 is formed withy aeXible end 4wall 42 connected to tube-31, andi tuning adjustment screws 43 are provided to react between a mount 44 rigid with tube 31 and a lug 45 rigid W-iththe body of resonator 36. Resonator 35 is also provided With a flexible yend vWall I6V secured to tube 31, and tuning adjustment means (notshown) may be provided for resonator 35. Also, if desired, 'gangtuning mechanism similar to that dis-` closed inLetters lPatentNo. 2,311,658 maybe employed vfor 'proportionately-.tuning resonators 3,5 and 36. Input grids 41 andi48 areprovided for resonator 35, and loutputgrids 49 and5l 'are provided fo'r resonator 36 in the electron -beam path.

As illustrated, `resonator 36 is smaller-than resonator, 35, ,and so may betuned tofhigherresonant frequencies. Device34 isla frequency multiplier wherein reonator 36 is,L capable. of tuning adjustment until its natural. frequency is a harmonic'of a resonant frequency of .resonator 35.

yAsource of voltage; having a constant frequencylsprovided as-indicated at 5'2. This source may bea `conventional crystal-.controlled oscilf,1 lator capable of extremely. accurately maintaining a fixed relatively, low frequencyv output, this xed; frequency v,in la preferred embodiment of the invention being 3.v75.,megacycles (mc.) per second; This fixed frequencyqoutput is delivered bya coaxial Yline,.53 toa frequency multiplier chain unitp54 ofvv conventional type wherein that fixed .frequency is .successively quadrupled, then doubled, then tripled and nally .again tripled until'the frequency ofthe output voltage on co- -axiallfline 55is 27.0 megacycles per second. Line 55:isconnected to serveffas the input for excitation of the field in resonator 35, the resonant frequency of resonator 35 being 270 megacycles per second., A coaxial output line is provided at 56 for extracting energy :from vresonator 35.`

:Source 52. is coupled yby coaxalline 51 to a frequencyquadrupler 53, and the megacycle per secondV output of the latterappears across the primary :59 of la coupling transformer. The transformer secondary 60 anda-variable condenser 6I provide a tuned input circuit bywhich the v15 megacycle voltage is impressed vbetween grid A62 and vcathode 63 ofa triode 64. =A condenser 65: and Aparallel inductance 66, forming a tuned circuithavinga resonant frequency twice that of circuit 60, 6l., are connected intheplate-circuit'of triode-.64 in series with a variable potentiometer 61 which is suitably dis` posed across a convenientb'atteryor like source 68 -ofl plate current for triode B4, as illustrated. The -alternating current circuitY of triode 54 is completed to'groun'd throughk by-pass condenser Triode 64 is operated to function as a yfrequency doubler whereby the alternating signal appearing on line 1IY ,has -a frequency double that of the input to grid 62. This megacycle per second output of 'f triode 64 is impressed between cathode 38, andgridAl which is connected `to ground throughl the :conductive Walls ofl cavityA resonator 34.

The :unidirectional .l accelerating voltage for producing an `electron beam from cathode v38 forvv projection through grids ,41, 48, 49 and 5I4 is providedlb-y -a suitable source indicated at 12. ,This accelerating vvoltage is modulated by the alternating-voltage` on line 1I. A- blocking condenser 13 keeps this direct voltage.V

out of the modulator circuit-14.

Theabove described arrangements for obtainingthe recited frequency relations represent only a preferred manner of accomplishing the same, it beingapparent that any equivalent manner of obtainingharm'onically related input resonator and electron beam modulation` frequencies lies within the scope of theinvention, as will be determinedin the claims. A decided advantage of the above describedarrangement, however, is that bothv multiplier units 54 and1'58function as buffer stagesffor preventing disturbances" in cavltyresonator device 34 from affecting kthe source frequency. Also use .of the same'source frequency for bothl the modulating and input frequencies simpliers. control problems.

In normal operation, the electron beamfrom cathode 38 is subjected to velocity modulation'and electron grouping similarly to the amplifier of Fig. 1, and resonator 3,6 may extract energy fromy the velocity grouped beam at an'output frequency which is a harmonic of the frequency ofthe inputl (270 mc.) frequency of resonator 36. Such frequency. multiplier operation in general isvknoWn anddescribed in Hansen et al. Patent No. 2,281,-

935 to which reference'is made for further; detail.

In the illustrated device 34, by suitableadjusttentlr eleventh and twelfth harmonics of the input frequency to resonator 35. 1

Thus normally four separate separately'available from device 34 during its normal tuning rangen These four frequencies are; indicated by solid lines F9, F1o, F11 and F12 in'Fig.-

5, and will be referred to as vthe carrier frequencies available .in theoutput of :device 34.sinceA they `correspondto normal frequency F of the device ofFig.`-1.

Through my invention, the number ofV frequencies available for extraction from resonator' 36 is greatly increased .Without mechanical or physical changes in the cavity resonator device 34.

Variation of the.- electron beam acceleration.

voltage, as by the 30 megacycle per second modulating signal introduced on line 1l, correspondingly varies the transittimes of the electrons in the beam. This correspondingly variesk the phase ofthe resulting electron .concentrations relative to the input resonatorY field, and thus produces' phase modulation of the electron grouping in the beam, similarly to the operation described above for Fig. 1. grouping is phase modulated at a relatively low frequency which is rationally related to the bunching or velocity modulating frequency. By rationally related, lit is meant that the ratio of theV carrier or velocity-modulating frequency to the modulating signal frequency is lan;,integerY or-a quotient of integers. The bunched electron beam is therefore phase modulated approximately in" proportion to the alternating modulating volt-` age impressedon cathode 38. y

These modulation effects produce'an available output from the phase modulated grouped beam which consistsof a number ofcarrier frequencies (harmonics of the input frequency toL resonator 35), each having an infinite number of sum-and difference sideband frequencies spaced at intervals corresponding to the frequency vof, the modulation voltage online 1I. Suitable tuning of resonator 35 makes available on line 55 anyg,

of these frequencies. It is desirable and preferable to have the modulation frequency a -subharmonic of the exciting frequency ofresonatory 35. This will insure that the sidebands of, one harmonic of the buncher-frequencycoincide withY and* reinforce theamplitudes of theA sidebands., of other harmonic frequencies, 1 and thereby will.;

frequencies Y are f In thismanner the electron beam.

amasser prevent occurrencebf scattered sideband's of: low

amplitude. at undesired frequencies within the An integral number ofisidebandsl tuningirange; is thus produced betweeneach pair'off adjacent harmonics.- within the'. tuning; rangev of resonator 36; I have foundthat the choiceof an odd sub-harmonic of the input frequency for'V the modulation.` frequency is'preferabley sincel iti. de creases" the` interi/alf betweensidebandsV when the numberfof sidebands is limited by the possibleY output at. those sideban-ds.

Whileldevices l may be an amplifier and1function-according tothe invention' as explained in Fig'. 1'; itis preferablya frequency multiplier becausef the ylatter has better.' frequency stability described modulation frequency of Somegacyclesper: second was chosen` only because. ity rwas vsuiii-A centl'yv high.. soV that thecarrier and sideband frequencies- Were'` readily separable' and obtainable by tuning" over the range of resonator 36';

In Fig. the Solid lIlSFs, F1o, F11 and Flaindicate the' harmonic. orf carri-er frequenciesA available from.' resonator 36. These areth'e harmonics thatcorrespond'to. frequencies 2430, 2700, 2970 and3240fmegacycles per second" and'occur with no'm'odulation' voltage; The varioussidebands arerspacedl apart by 30megracycleaandl are indicated by thedotted lines in Fig. 5. Asfurther illustrated in Fig. 5, the sidebandsthus-produced arerofl substantial and almost equivalent amplitude:

The-:resonator device. of! Fig; 4 is prepared for operation. by suitable energization' and prelim'- inary adjustments to obtain the proper exciting,

and modulation frequencies, the desired acceleration Voltage on the' cathode, and tuning of resonator 35 to,` one of' it's'resonant frequencies.`

Only two'radjustments are necessary after thesev preliminary adjustments have beenfmade; First resonator! 36! is' tuned untilv the desired output frequency, carrier or sideband; is obtained' in line' 'I'hen the plate: Voltage of modulator tube 56; 6422 is varied Aby. ypotentiometer 5ll until the lowest modulation'fvoltag'e giving maximum amplitude inthe: output' of resonator 36 is obtained. The

potentiometer can be" calibrated'so" as to indicate tliese:v optimum modulation voltages" for eachoutput freq'uenclfx,V and the-tuning mechanis'm :canrbecalibrated inzterms of sidebandsrand r carrier frequencies:

Iii-desired; theramplifler of Fig; 1v may derive itsin'put" resonatorr and modulation frequencies fromfacommon. source, .as in` Fig. 4; or the'input crystal controlledv source`,.for eacli' output fre-r` quency;

Thevsidebands should be atleast 3L megacycles apart? forfnormal cavity resonators, but wheref very-high Qresonators are employed sidebands only 100-kilocycles apartlmay be separately,v ob"- tained.

use las' afre'quencys standard; the apparatus ofi the" invention' may" be` used for calibrating` wavemeters; It'v may also be used as4 a stand'- arid l directly.- in the following,Y manner. First,` measure? the'. unknown frequency fr approximately by? a wavemeter; andy adjust the" appara-F uis 'of'.tlie :invention to 1 producer thecloseststandardifrequencyfe.. Tl'ienl introduce bothhfa.- and'` fx: into.` a1 crystal rectifier mix-er of known type; soas tof produce-1 a2 differenceI frequency output'. This'.r difference. frequency-g. which, .for example,4 .with the: apparatus ofFia; 4

will always bei less than 30S megacyc'le's pen second; can; then; bei measured. by: any; conve-nient'4 knowny manner of accurately measuring': friequencyf inA this-Triangel Besides serving: as: aV frequency standard for calibration andy measurement'- purposes the ap'- pa'ra'tulslof'y the invention may.' be used as? ai signal generator, as? a. source: off power4 to replace a. local `oscillator;with:l af stable. frequency, and like'- applications.` llliso;4v wherei higher; standard fre:- quenciesa-re desired; theoutputmay becoupled to a suitable? ultra! higlilffrequencyf multiplier;

Other possible: combinations-. ariel available: for'- obtainina almostg any.' 'desired'. stendardi-frequency;

In'stead of' pr'ovidingf ai modulation: voltage' oni:4

the cathode` or'-A someothery beamf control electrode, the f same. results'can' be' f obtained:v by! phase: modulating` the 'output ofsource's i3 l `orf52 ins'uchi manner thatf botlr velocity andiv phase:v modula'# tion of.tine-electroni` beam is accomplished byfits interactioni with the? eld! within resonator: 35;- This would enable the: modulator# unit I4- to be eliminated.`

Furthermore; the: inventioni p'ovides a goodb frequency sourcei fori use? in` either' or' boththe:

transmitter andi receiver?v in'.l ab multi-channel provide a selective soumet of many? transmitter frequencies;A and the.` receiver could beisimilarly arranged: andI controlled. l

Since.` many changes could."y be.' made' mathe" above construction" and z many apparently. Widely different.y embodiments 0f this: inventionv could be made; withouti departing; from the'. s'copie thereof, it! is-'intended that alli matter contained in. the abovel description or lshowninithe'. accom panying; drawing: shall' be` interpreted as illusr trative and not in a limiting sense. ,i

What is-claim'e'diss` l'. Ultrahigli frequency apparatlis'coinprising means for:` provldin'g' am electron beami. having'.A

electroni groupirigf tliere'alng at a", rate of' repetitionl corresponding? to a2 carrier frequencyy means fori-I producing phase-.rnodulation ofi 'saldi` electron'. grouping' ati a'. predeterminedfV modulation lfrequency; and.'E means'` for: e'x'tractingienergy a multiple'of saidK carrier frequency by anfini tegral multiple ofl said Ymodulation frequency;

2 Ultra h'iglillfrequency apparatus comprising. means forY providing anA electron-1 beam having! electron grouping' therealon'g corresponding f to a.

vat a frequency which vis rationally related-to said 4grouping frequency, l and extracting alternating energy from said modulated beam. l

5. A method of 'producing high frequency energy which comprises the steps of producing elec-- -tron grouping in an electron beam at a rate of repetition corresponding to a carrier frequency, phase modulating said electron grouping at a fre'- quency whichvis a sub-harmonicof said grouping frequency, and extracting alternating energy from said modulated beam.

6. Ultra high frequency apparatus comprising means for providing a resonant circuit oscillating at a predetermined frequency, means for projecting a beam of electronsin energy exchanging relation with said circuitffor producing electron grouping along said beam, means for producing phase modulation of said electron grouping' at' a frequency which is rationally related to the frequency of said circuit, and means for extracting energy from said modulated beam.

'7. The apparatus defined in claim 6, wherein said modulation frequency is a sub-harmonic of the oscillating frequency of saidcircuit.

8. The apparatus definedin claim 6, wherein said modulation frequency is, an odd sub-harmonic of the oscillating frequency of said circuit. v

9. Ultra high frequency apparatus comprising means dening a resonator adapted to provide an oscillatory electromagnetic field, means for projecting an electron beam through vsaid field to produce electronugrouping along said beam, modulating means for varying the flight time of "said electrons at a modulation frequency which is a sub-harmonic of the frequency of said field, and means for extracting energy from said modulated beam.

10. The apparatus defined in claim 9, wherein said modulation frequency is an odd sub-harmonic of the frequency of said field.

11. A method of producing high frequency energy which comprises the steps of projecting an electron beam through an oscillatory electromagnetic field in such relation therewith as to produce electron grouping along the beam,

varying the beam acceleration voltage for Varying the flight time of said electrons at a modulation frequency rationally related to the frequency of said field, and extracting alternating energy from said beam by interaction of the beam with a tuned resonant circuit.

12. The method defined in claim 11, including the step of varying the average beam acceleration voltage for obtaining optimum output at the frequency of said alternating energy. l 13. A method of producing high frequency energy which comprises the steps of modulating an electron beam to produce electron grouping therealong at a carrier frequency, phase modulating said grouping at a modulation frequency, and controlling both said carrier and modulation frequencies from a common source.

14. An ultra high frequency system comprising a frequency multiplier device of the cavity resonator ty-pe,-cathode means adjacent thereto for projecting an electron beam through said device, a source of fixed relatively low frequency, a frequency multiplier unit connected to said source and to said device for delivering input field energy to said device at a frequency which is a relatively large multiple of said source frequency, and a second frequency multiplier unit connected to said source and to said cathode means for modulating the driving voltage of said 10 electron beam at a frequency which is a lower multiple of said source frequency. 1,5. The system defined in claim 14, wherein said second frequency multiplier unit comprises an electron discharge device having a plate electrode, and means for varying the plate current through said l.electron discharge devicegforde- ,termining maximum amplitude of'output for said frequency multiplier device at its operatingfrequency." .t ,y r r 16. In a method of selectively obtaining one of an integral sequence of stable frequencies, the steps of.,producing electron grouping Iin an electron beaml at a rate of repetition corresponding to Aa .carrier frequency, phase modulating said grouping at a modulation frequency, coupling said modulated beam to a resonant circuit, and tuning said circuit to resonance at a frequencywhich diners from a harmonic of saidcarrier frequency by an integral multiple of said modulation frequency. .f

17. The methoddened in claim 16, wherein said modulationfrequency is a sub-harmonic of the carrier frequency.. Y y v 1 18. A method ofproducing high' frequencyl energy which comprises'the steps of velocity modulating an electron beam to effect velocity groupiingA of the electrons therealong at a carrier frequency, phase modulatingv said ygrouping at a modulation frequency, and extracting alternating energy from said beam ata frequency whichfdiffers from'a harmonic of said carrier frequency by an integral multiple of said modulation frequency.

y'19. A method of producingr hiehlfrequen'y' er1- ergy ,which comprises the `steps of producing a carrier frequency wave phase-modulated by a modulation frequency which is a subharmonic of said carrier frequency, velocity modulating an electron stream in accordance with said modulated wave toeffect velocity grouping of the electrons therealong, and extracting alternating energy from said stream at a frequency which differs from a harmonic of said carrier frequency by an integral multiple of said modulation frequency.

20. A method of producing high frequency energy which comprises th'e steps of producing a carrier frequency modulated by a modulation frequency which is a subharmonic thereof, grouping an electron stream in accordance with said modulated carrier1 frequency, and extracting alternating energy from said stream at a frequency which differsfrom a harmonic of said carrier frequency by an integral multiple of said modulation frequency.

21. A method of producing high frequency energy which comprises th'e steps of grouping an electron stream in accordance with a carrier frequency modulated by a modulation frequency, and extracting alternating energy from said stream at a frequency differing from a harmonic of said carrier frequency by an integral multiple of said modulation frequency.

22. 'Ultra high frequency apparatus comprising a frequency multiplier device having a fundamental frequency cavity resonator, a tunable harmonic frequency cavity resonator, and means for producing an electron stream coupled to said resonators; means for supplying carrier frequency energy to saidfundamental frequency resonator; and means for modulating said stream in accordance with a modulation frequency, said harmonic frequency resonator being tuned to la frequency differing from a harmonic of said carrier frequency by an integral multiple, including unity,

of said'. modulation frequency, Wherebyenergy of said tuned frequency lmay be'extracted fromsaid stream;

23.. High' frequency apparatus comprising afrequencymultiplier device having a fundamental tunedA circuit, an output tuned circuit tunable over a--rangeof harmonics. of said fundamental frequency,v and .means for producing` an' electron stream coupled to said circuits; meansforsupplying an input Wave to said funda-mental frequency tuned circuit including a carrier frequency modulated'by a'modulation frequency Wh'ichis a sub- `harmonic'of said carrier frequency; and means for tuning said output circuit to a frequency `differingffrom a harmonic of said fundamental frequency by an integral multiple of said modulation frequency, whereby energy of said tuned frequency may be obtained from said apparatus.

24.- High frequency apparatus comprising an electron discharge device having an input circuit tuned to a predetermined fundamental frequency, az-tuned output circuit tunable over a range of harmonics of said input circuit frequency, and means for producing an electron stream coupling said*l circuits; means for supplying a carrier frequencyto vsaid input "circuit of substantially'V said fundamental. frequency; means for modulating said' stream at a modulation frequency; and means'for tuning said output circuit to a frequency differing from a harmonic of said carrier frequency byzan integral multiple of said modu- 'lation frequency, saidmodulation frequency being greater than the band Width of said output circuit, whereby substantially only a single frequency Will be extracted from said stream.

25.V Ultra high frequencyfapparatus comprisingj an electronydischarge Adevice having `a fundamental frequency; cavity resonator and an output cavity resonator separated by y'afield-free drift space, vandmeans forcoupling said resonators, by an electron, stream; means Vsupplying a carrier frequency Wave of substantially ysaid fundamental frequencyv to said'funda'mental frequency resonatorV to .velocity modulate and to produce yelocity'grouping; of said electron stream at said carrier frequency,v means for'modulating saidgrouped.v electron; streamV at a modulation frequency, said output resonator Ybeing substantially'tuned to av frequencyfdiiering from a harmom'c ofsaidcarrien frequency by an integral multiple ofjsaid modulation frequency, whereby energy'of said `tuned frequency maybe extracted from'said-stream.

26. Apparatus'as` inV claim' 25, wherein: said modulation frequency has` azvalue greater than the band Widtliof said outputzresonator.

ARTHUR; E; HARRISON.

REFERENCES CITED The following'references are Aof record in the file of this patent:

UNITED STATES PATENTS Number 

